Method of producing composite metal stock



4, E945. w. A. MUDGE 2,399,452

METHOD OF PRODUCING COMPOSITE METAL STOCK Filed Jan. 19, 1943 INCO/VEL CLRD* commen@ N/CKEL DlFFU/o/v ZONE JNVENTOR. v. w/u/HMH/.l//NMUDGE El@ 5' msm i ATTORNEY Patented'Dec. 4, 1945 UNITED STATE METHOD OF Pnonoonvo COMPOSITE METAL s'rock New York, N. Y., assignor Nickel Company, Inc., New York, N. Y., a corporation of Delaware Application January 19, 1943, Serial No. 472.838

William Alvin Mudge, to The-International 6 Claims.

The present invention relates to a process for producing composite metal stock and more particularly to a process of cladding a base metal such as plain carbon Steel or low alloy steel with a corrosion-resistant and heat-resistant metal or Canada November 26. 1942 (Cl. Ztl-189) alloy such as the stainless chromium-containing alloys of iron and nickel.

Many attempts have been made to weld sheets of chromium-containing alloys to steel plates by heat and pressure. strated that it is not possible in commercial practice to obtain a satisfactory bond directly between a stainless chromium-containing alloy and a steel base by the application of heat and pressure.

` An early attempt to improve the bond between stainless steel and a steel base comprised inserting a thin sheet of high purity iron between the base metal and the cladding metal before heating and rolling. This expedient, while it gave better results than the process in'which the cladding metal was placed in direct contact with the steel base, still failed to produce consistently satisfactory results. l

A further development comprised the electrodeposition of a protective metal on the thoroughly cleaned surface of the chromium-containing clad sheet and then placing this protectively coated surface against the cleaned surface of a steel base plate for heating and rolling. Satisfactory results have been obtained on a commercial scale in this manner but the process is somewhat cumbersome, expensive, and requires the installation of large electroplating apparatus. Rolling mill plants not equipped with electroplatlng apparatus have been forced to have the chromium alloy plates coated with the layer of protective metal outside of their own plants, sometimes even in other cities.

Although the art has recognized the need for a commercially satisfactory process that can be carried out in rolling mill plants which were not equipped with electroplating apparatus and numerous attempts to solve the problem have been made, none of these, so far as l.' am aware, has succeeded in commercial operations on an industrial scale.

I have invented a process of welding corrosion resistant metals and alloys such as corrosion resistant chromium-containing alloys of iron and nickel to less noble metals such as steel which avoids the cumbersome, expensive and time-consuming step of electrodepositing protective metal on the sheet or plate of corrosion resistant cladding material before it is assembled in a pack Experience has demonwith the foundation metal. In accordance with my invention a lm of protective metal in finely divided form in a suitable vehicle is applied to the clean surface of the corrosion resistant metal that is to be bonded by heat and pressure to the steel or other foundation plate.

It is an object of my invention to provide a process for producing composite metals having a heat-resistant clad firmly bonded to a less noble foundation metal.

It is another object of my invention to provide a process of producing steel clad with a stainless chromium-containing alloy on standard rolling mill equipment without having to use expensive electroplating apparatus or other costly equipment to prepare the surface of the chromium-containing clad for the welding operation.

It is a further object of my invention to provide a simple process for preparing the surface of a heat resistant clad for bonding by heat and pressure to a steel foundation layer which involves painting or otherwise covering a clean surface thereof with a protective layer of finely divided metal or alloy in a suitable volatile liquid.

Other objects and advantages of the present invention will become apparent from the following detailed description thereof taken in conjunction with the drawing in which:

Fig. l represents diagrammatically a section through a single pack prepared for the welding operation in accordance with the present invention by painting' the surfaces to -be bonded with metal powder in a suitable vehicle and superposing the layers to form a. single pack;

Fig. 2 depicts diagrammatically a section through a multiple pack composed of two single packs superimposed with their cladding layers contiguous but separated by a parting compound: and

Fig. 3, which is reproduced from a photomcrograph of a polished and etched section of the welded pack taken at a magnification of diameters, shows how the powdered nickel has consolidated and diffused into the chromium-containing clad and the steel foundation layer to form a strong bond.

Generally speaking, the process of the present invention comprises covering a surface of a corrosionor heat-resisting metal clad with a protective layer of metal powder suspended in a suitable vehcle, placing the protectively coated surface in contact with a surface of a foundation layer of a less noble metal to form a pack, heating the pack to a welding temperature and applying pressure to the heated pack to form a firmly bonded composite metal stock.

Any suitable metal may be used for the foun- ,lmzign layer including plain carbon steel, alloy steel, copper, copper alloys andv the like. The vcladding metal preferably is a chromium-containing euoy with a sumeientiy nigh chromium content to make the cladding metal highly resistant to heat, to corrosion and oxidation. Among the commercial chromium-containing alloys contemplated are the 60-15-25 nickelchromium-iron types and the 80146 nickelchromium-iron types sold under the trade-mark Inconel, and stainless steels, particularly types 304 (18Cr-8Ni), 309 (25Cr-12Ni), V310 (20Ni- Cr), 311 (25Ni-20Cr) and 330 (35Ni-15Cr). The process of the present invention may also be applied to other corrosion resistant metals such as nickel, nickel alloys, including nickel-copper alloys of this type sold underthe trade mark l Monel, and the like. A clean surface is provided on the cladding metal in anysuitable manner, e. g., by grinding, pickling, etc., so that the surface is free from any oxide or other f ns which might interfere with welding by heat and pressure. The clean surface is then protected against the re-formation of an oxide or other weld-preventing iilm by coating it with finely divided protective metal in a liquid vehicle. The protective metal powder preferably is in iiake form and the suspension may be applied by brushing or spraynegligible amounts of water vapor upon heating under restricted access of air, may also be used. However, if the vehicle contains any moisture or if water and/or other oxidizing agents result from evaporation or decomposition of the vehicle, they should be of such quantities that the resulting ratio between the reducing constituents and oxidizing constituents thus produced will -be sufilciently high that the degree of oxidation, if any, of the surface of the foundation layer and/or of the surface of the cladding layer will not interfere with proper welding. Thus, Inconel-clad steel may be produced by using flakenickel applied in a vehicle consisting of orange shellac diluted with synthetic methyl alcohol. When the nickel flake-shellac-alcohol mixture isapplied to Y the metal surfaces and allowed to dry; the alcoing the mixture on like a paint or the clad may be dipped into a vessel containing the mixture. Preferably. the laver will have a minimum thick'- ness of about 0.015 inch although this thickness is not critical and satisfactory results may be obtained with even thinner layers. A single coat of the protective metallic paint may suiice but in some cases it may be found desrablelto apply a plurality of coats of the same or differentmetallic flake paints.

The protective metal should be one that bonds readily by heat and pressure to both the Abase metal and the clad. When the base metal is steel and the clad is a chromium-containing'alloy yof iron and/or nickel, Ythe protectivedafyer preferably is composed of nickel flakes.I the clad may be coated with a metal that does not readily Weld to the base metal by coating the latter with metal that bonds readily to the base and the protective coating on'the clad. Other metal powder that may be used with satisfactory results include aluminum, cobalt, copper, iron, silver and the like or alloys or mixtures of these metals. W'hile the flake form of metal powder preferably is employed, powder produced by the decomposition of carbonyl, electrodeposition, grinding and like processes will also give acceptable results. It is essential that the vehicle used in making the metallic paint be one that will not produce an oxidizing atmosphere upon volatilization or decomposition thereof. Preferably, it is essential that the vehicle be substantially free from moisture and that water will not be formed, upon volatilization or decomposition thereof. Kerosene is one of the vehicles that have been used satisfactorily for this purpose. Other aliphatic hydrocarbons including low-melting-point parailins, aromatic hydrocarbons such as toluol, etc., may be used in place of or in combination with kerosene. Volatile aldehydes and ketones and other organic materials including certain lacquers which decompose into products such as hydrogen, hydrocarbons, carbon monoxide and Substantially In some cases hol evaporates practically entirely. `Most of the water that may be of coated steel surface. ItV may therefore be considered that the conditions existing at the int'erfaces .in the pack during the heating prior to rolling, approximate `the conditions extant in the combustion of organic hydrocarbons (shellac andV to oxidizing constituents (carbon dioxide and f water vapor) is so high that l a reducing atmosphereand reducing conditions are maintained at the interface between the Inconel and steel surfaces.

After the o1ean surface of the cladding metalV has been provided with the protective coating of metallic flakes, the vehicle may be Vallowedv to evaporate before placingthe protectively coated layerI in contact'with a clean surface of the foundation metal to form a unit or pack. It is not essential that the vehicle be completely evaporated but the coating should be suiiciently dry that it does not tend to run during handling of the plate. It will be understood, of course, that the foundation layer may be clad with the corrosion-resistant metal on one or both surfaces and, if desired, the surfaces of the foundation metal may be protected in the same manner as already described for the cladding layer. Ordinarily, however, it is not necessary to apply the protective coating on the base metal if adequate protection against oxidation thereof is provided during the heating operation.

A pack I prepared in this manner is illustrated diagrammatically in Fig. 1 in which reference character 2 represents the base or foundation layer having a clean surface 4, and numeral 6 designates the clad which has a clean surface 8. The protective layer of metal powder which was applied as a suspension in a volatile vehicle is shown at I0, its thickness being exaggerated for purposes of illustration, and it will be understood that layer I0 may be applied only to the surface 8 of clad 6 or also to the surface 4 of base 2. The adjacent edges may be welded as at I2 or otherwise secured to hold the pack together preparatory to the application of pressure. The weld bead I2 must not be continuoussince outlets must be left may be contained in the alcohol, which the order of one per cent, will evaporate with the alcohol. When the coated metal surfaces Y are brought together very little air isleft in the v space between the coatedlnconelsurface and the.

\ parting compound Wpared inihismanner tions. In this manner aecomo for the escape of residual amounts of the vehicle from between the base 2 and the clad B.

In some cases it is advantageous to heat and roll or otherwise hot-work a plurality of single packs simultaneously and Fig. 2 illustrates diagrammaticaily a multiple pack which has been prepared for this purpose. The single packs are prepared in the manner described above and the reference numbers represent the same parts as already described in connection with Fig. 1. Two such single packs are shown superimposed with their clad surfaces contiguous but separated by a it of some inert non-fusible oxide such as A1203, Me@ or similar material. The parts may be secured together, e. g., by welding as indicated at it. Any desired number of units pre'- may be superimposed for the heating and rolling operations' taking care to separate layers that should not weld together by parting compound.

After the pack has been ner, it is heated to a suitable temperature for the welding operation under such conditions that oxidation of the contacting surfaces is prevented. rllhis may be accomplished by using substantially continuous welds il, leaving only small vents for the escape of gases from the space between the layers, or the heating may be carried out in a furnace provided with a protective atmosphere, or the pack may be enclosed in a sheet metal container which is substantially air-tight except for small vent holes to permit the escape of the vehicle which is volatilized and driven out from between the layers of the pack by the heat and pressure.

The pressure may be applied in any suitable manner, e. g., by a hydraulic press which will apply pressure within the furnace or the pack may be removed from the furnace after heating and subjected to forging or hot rolling operaa very satisfactory bond is obtained between the cladding metal and the foundation metal which successfully resists separation of the layers when the composite stock is bent, twisted, stressed in shear, and tension.

In order to acquaint with the vantages .of the present invention, the following specic examples are given.

Example No. l

Two plates were cleaned thoroughly by pickling in acid. One of these was a plate of nickelchromium alloy containing about 80% nickel, 14% chromium, and 6% iron about 0.5 x 16 x 28 inches and the other was plain carbon steel plate about 3 a 2l x 33 inches. Three coats of a nake nickel powder mixed to a thin paste with kerosene were applied to one of the broad surfaces of the nickel-chromium alloy plate and allowed to dry overnight before the pack was assembled. The protectively coated surface was then placed in contact with the clean surface of the 1 lain steel plate to form a pack which was then hea ted under non-oxidizing conditions to a temperature of about 2250 F. For these metals a temperature within the range of about 20002300 F. gives satisfactory results. The heated pack was then subjected to hot rolling and reduced to a slab about inch thick by 30 feet long. A very intimate bond was produced which successfully resisted separation under tensile tests, double cold bend tests, twist tests, chipping tests and special shear tests. Microscopic examination disclooed that the flake nickel powder had compacted and developed a well dened grain structure, forming prepared in this manthose skilled in the art 45 a layer several thousandths of an inch thick free from voids. A nickel-iron alloy layer had formed between the nickel and the steel and a diffusion sono was also evident between the nickel and 5 nickel-chromium alloy layer. Fig. 3 of the drawing illustrates the type of bond produced by the process of the present invention in which the various layers referred to hereinabove may be dis- Example No. 2

v' A sheet of nickel and a sheet of nickel-chromium alloy similar to that of Example No. 1 were cleaned in the same manner as Example No. 1 and protectively coated by spraying nickel ake powder in a kerosene vehicle on the clean surfaces. Only one coating was applied and it was thinnerthan the coating applied in Example No. i. These sheets were then assembled with two plain carbon steel plates into a multiple pack similar to that illustrated in Fig. 2. The finished pack was about 6.68 inches thick by 29 inches wide by 47 inches long, one half of the pack being 10% nickel-clad steel and the other half was 10% nickel-chromium clad steel. The pack was then heated to a temperature within the range of about 2000 F. to 2300 F. and hot rolled in conventional manner to produce composite plates dimensions of about 68 by 120 inches.` Tests on about 0.25 inch thick which were cut to finished dimensions of about 68 by 120 inches. Tests on these composite plates, including bend tests and tensile tests, indicated that the results were satisfactory and comparable to those obtained in Example No. l...

Although the present invention has been described in conjunction with certain specific examples, these are to be construed as illustrative of rather than as limitations upon the process which is capable of modification and variation as those skilled in the art will readily understand. Thus, the invention can be applied to composite plates, sheets, slabs and the like iiat shapes to which pressure can be applied by a heavy weight, a press, or by forging, rolling, etc.; to cylindrical shapes such as composite wire, rods, bars, tubes and the like. to which pressure can be applied by rolling, drawing, extrusion, etc.; and to any other composite shapes which lend themselves to m the application of heat and pressure to produce a bond. These and other modifications are to be construed as coming within the spirit and scope of the invention as dened in the following claims.

l. The process of producing a composite metal having a steel foundation layer and a cladding layer of nickel-chromium-iron alloy firmly bonded thereto, which comprises cleaning a sur- 60 face of the nickel-chromium-iron alloy layer to remove any oxygen or other weld-preventing film, preparing a paint of nickel Flake powder in a kerosene vehicle, applying a coating of the paint on the clean surface of the nickel-chromium-iron alloy layer, placing the coated sur- 65 face of the cladding layer against a clean surface of the steel foundation layer to form a pack, and

subjecting the pack to duce a bond between the foundation ding layers.

2. In the process of heat and pressure to proand cladproducing composite metals having a steel foundation layer and a cladding layer made of an alloy containing about 5% to about 35% chromium and at least 50% nickel which involves pickling a surface of the cladding 45 layer to remove any oxygen or other weld-preding layer of an alloy of chromium with a metal the foundation layer through an interposed layer venting lm and bonding said pickled surface of said cladding layer to Isaid foundation layer through an interposed layer of metal by heating the assembly to a temperature within the range of about 2000 F. Vto about 2300* F. and hot 5 rolling the heated assembly to produce a bond between the cladding and foundation layers, the improvement which comprises applying a coating of nickel flake powder in a kerosene vehicle to the pickled surface of the cladding layer and assembling the cladding layer and the foundation layer in a pack with the protectively coated surface of the cladding layer in contact with the foundation layer. l

3. The process as set forth in claim 2, in which the surface of the foundationilayer which contacts the protectively coated surface of the cladding metal is" cleaned and coated with nickel flake powder in a kerosene vehicle before the layers are assembled in the pack.

4. In the processV of producing composite metals having a steel foundation layer and a cladlected from the to a surface of the cladding pack to heat tween the cladding and foundation layers.

from the group consisting of nickel and iron which involves pickling a surface of the cladding layer to remove any oxygen or other weld-preventingV llm and bonding said pickled surface to of metal, the improvement which comprises applying to the pickled surface of the cladding layer a coating of metallic powder selected from the group consisting of iron, nickel, cobalt, copper, silver and aluminum in a liquid volatile organic vehicle that does not produce an oxidizing atmosphere upon volatilization or decomposition.

cobalt, copper, silver and aluminum.

WILLIAM ALVIN MUDGE.

CERTIFICATE or CORRECTION. Patent No. 2,59o,ii52. December il, 19Lt5.

WILLIAM ALVIN MUDGE It is hereby certified that error appears in the printed specification o f the above numbered patent requiring correction as follows: Page 5, second column, line 29, Exemple No. 2, strikev out the words "dimensions of about 6 8 by 120 inches. Tests on"; and that the said Letters Patent should be read withthis correction therein that the same may conform to the record of the case in the-Patent Office.

Signed and sealed this 19th day of March, A. D. 19146.

Leslie Frazer (Seal) First Assistant Commissioner of Patents.

5. The process of producing composite metals having a foundation layer selected from the group consisting of carbon steel, alloy steel, copper and copper alloys, and a cladding layer segroup consisting of nickel, f nickel-copper alloys. nickel-chromium alloys, nickel-chromium-iron alloys and stainless steels, which process comprises applying a protective coating of metallic powder in a liquid organic vehicle which does not produce an oxidizing atmosphere upon volatilization or decomposition layer, said metallic powder being selected from the group. consisting of iron, nickel, cobalt, copper, silver and aluminum, assembling the protectively coated cladding layer in a pack with the coated surface in contact with the foundation layer-and subjecting the and pressure to produce a bond be- 6. In the process of producing composite metals having a metallic foundation layer containing copper and a cladding layer of chromium alloyed with metal from the group consisting of nickel and iron which involves bonding said foundation layer to said cladding layer through an interposed layer of metal, the improvement which comprises .applying a protective coating of metallic powder vin a liquid organic vehicle which does not produce an oxidizing atmosphere upon volatilization or decomposition to a surface of the cladding layer, said metallic powder being selected from the group consisting of iron, nickel, 

